This invention relates to the manufacture of pneumatic tires for automotive vehicles especially to the post-cure processing of such tires to assure dynamic uniformity. More particularly, the invention relates to a method and apparatus for reducing variations in lateral force and overturning moment and to the combination of that function with the function of reducing radial force variations, both in a single convenient post-cure operation using equipment easily adapted from tire uniformity correction machines such as that shown in U.S. Pat. No. 3,724,137.
Existing tire uniformity machines for correcting radial force variations in pneumatic tires generally comprise split rim sections on which a tire is mounted and then inflated to specified pressure. The inflated tire is rotated at a specified operating speed while deflected by a loading drum adapted to apply a predetermined radial load against the tire. The loading drum is mounted for free rotation about its axle and variations in radial force experienced during rotation of the tire are sensed and measured by load transducers as disclosed in the U.S. Pat. No. 3,724,137.
Rotary grinders, positioned adjacent to the shoulders of the tire tread, are moved together into grinding engagement with those portions of the tread where excessive positive force variations have been detected. The rotary grinders consequently remove sufficient material from the tread shoulders to reduce the magnitude of the force variations to an acceptable level.
Certain customers specify lateral force variation values as well as radial force variation values. Tire uniformity correction machines adapted to reduce only radial force variations to an acceptable level do not change lateral force variation values. In some instances, lateral force variations can exceed customer specification limits and in these cases the tires may not be supplied to this customer.
The method and apparatus of the present invention, however, provide for more effective tire uniformity by reducing variations in lateral force and overturning moment as well as variations in radial force and also afford other features and advantages heretofore not obtainable.